Optical studies of two biophysical model systems: Vesicle deformation and DNA localisation in yeast

We have looked at two model systems commonly used in biophysics and biology; giant unilamellar vesicles (GUVs) and the fission yeast Schizosaccharomyces pombe (S. pombe). GUVs can be deformed by short electric pulses in the presence of 80nm gold particles. This gives rise to cylindrical deformations, either tube-like or disc-like, depending on the conductivity ratio between the inner and outer vesicle solutions. Although the participation of the gold particles in the directionality of the deformation is unclear, we have shown that they are likely to contribute to the flattening of the deformed vesicles

.We also studied the deformation of GUVs by means of optical tweezers.Repeated exposure to the focused laser light led to a decrease in vesicle size followed by the formation of vesicle aggregates. Vesicle size and the phase of its bilayer largely influences the degree of deformation at a given laser power. We believe that the observed deformations are due to the scattering force pushing the membrane in the direction of propagation of the light.

The last chapter looks at silencing in S. pombe. The heterochromatic part of the mating-type region in fission yeast is delimited by two so-called boundary elements, IR-L and IR-R. By replacing IR-R with a piece of rDNA a strong silencing of the mating-type region as well as its relocalisation closer to the nucleolus was observed. The distance in 3D between the mating-type region and the nucleolus was measured using a custom made Matlab program. We are currently investigating possible silencing mechanisms.

Supervisor: Lene Oddershede